1. Field of the Invention
This invention most generally relates to a heat exchanging device for heating a fluid such as air and is more particularly concerned with providing heated air by conduction of heat, at a plurality of locations, from a combustion gas space to the fluid. The combustion passage is substantially coextensive with but is not in air mixing communication with the fluid to be heated or the plurality of volumes wherein heat transfer occurs. Even more particularly the invention relates to a heat exchanging device for heating air wherein the combustion region is defined by two concentric cylindrically configured heat exchange surfaces, one surface being the inner shell of a coaxial heat exchange member and the other surface being an outer shell of the coaxial heat exchange member. The combustion chamber is contained within the heat exchanger and is defined by a truncated cone portion of the coaxial member and has an arcuate surface upon which a flame strikes and side walls which taper from a small circumference to a larger circumference creating a chamber having a cone configuration which taper approximates the cone shape of a flame emanating from a flame producing nozzle.
2. Description of the Prior Art
It would be desirable and advantageous to have a heat exchange device which would be capable of burning waste oil products efficiently and in a manner which would allow easy cleaning of the burner unit and the heat exchanger. It would also be desirable to have a unit or device which has the combustion take place within the heat exchanger instead of in a chamber removed from the heat exchange region. It is also important that the combustion flame not impinge directly onto a surface causing deposits to form which may result in the incomplete and inefficient burning of the fuel. It is also important that the gases of combustion be kept separate and in a non-mixing relationship and that these hot combustion gases be directed in such a manner as to encounter large surfaces which are in thermal contact with turbulent fluid, such as air or water, which is to be heated. To improve or enhance the efficiency of thermal energy transfer from the hot gases of combustion, the fluid should be turbulent close to the heat exchange surfaces.
In order to be able to burn waste oil products in an efficient and ecologically sound manner, it is critical that the combustion efficiency be within well defined specifications. It is required that the efficiency be not less than 75% as measured according to industry accepted standards of testing and that the residuals emitted be as completely oxidized as possible at this efficiency level. The maintenance must be low, the combustion efficiency high, and there must be high thermal energy transfer in order that the system be acceptable for such use. In particular, the design of a device for the burning (rapid oxidation) of contaminated waste oils should have a smooth uniform, constant, controlled flow of combustion gases throughout and there should be no abrupt direction changes of the gases while they are at the highest temperature, i.e., prior to the combustion gases giving up most of the heat to the fluid. This is necessary to uniformly deposit, within the device those noncombustibles inherently generated by this process. When this is accomplished the heat exchange degradation process is more nearly uniform preventing premature heat exchange loss in any given area.
It is also very important that the device can be quickly, easily and thoroughly cleanable. In the burning of waste oil those noncombustibles contained in the waste oil deposit in the combustion chamber. This material must be easily removed in order that the efficiency of the system be maintained.
The instant invention accomplishes such objectives. In accomplishing the objectives of efficient burning of waste oil, the device is also very effective and efficient and very maintenance free when burning conventional heating oil. Applicant is not aware of any heat exchanger devices or assemblies presently available which meet the necessary criteria for the proper and effective burning of waste oil products coupled with the ability to expose completely and in total all prime heating surfaces for necessary, periodical inspection and/or mechanical cleaning. Nor is Applicant aware of a device which incorporates all of these desirable features within the relatively small volumetric configuration possible with this invention. In fact Applicant is unaware of any such units available which have the advantages and characteristics described that burn regular fuels such as heating oil and/or gas.
Some inventions related to the instant invention and disclosed in the following United States Patents have been studied. The following is a brief description and discussion of these related inventions.
Wilson, U.S. Pat. No. 4,905,661 discloses cylindrical heat exchanger in which the flame is introduced into the device about perpendicular to the axis of the flow of both the combustion gases and the air which is being heated in the device. In the patented device, the combustion gases flow in a helical path around the inner shell through which air to be heated flows in an axial path through the device and the flame is introduced into the combustion chamber in a direction perpendicular to the axis of the heat exchanger.
Juhnke, U.S. Pat. No. 2,056,465 discloses a heater having a cylindrical shape and including a plurality of passageways for air flow therethrough, the passageways allowing contact with the combustion gases in a middle cylinder defined by the inner cylinder wall and an outer wall, the outer wall also in contact with the air and the combustion gases.
Tate, U.S. Pat. No. 483,819 discloses a hot air furnace which includes a central air passageway which contacts a middle cylinder containing the gases of combustion. The outer wall of the middle cylinder are also in contact with the air, providing two heated air masses.
Rice, U.S. Pat. No. 586,062 discloses a hot air furnace which includes a central jacket having a plurality of pipes having the shape of the frustrum of a cone. These pipes and the outer wall of the jacket radiate heat to the air masses outside the central jacket.
Muckelrath, U.S. Pat. No. 3,388,697 discloses an enlarged air heater for discharging large volumes of heated air toward outdoor work areas and the like comprising upper and lower tubular members within which bypassing non-communicating combustion and air passages are defined for progressively heating the air from the intake end to the discharge thereof. The combustion passage includes a fire tube and an exhaust chamber while the air passage includes a preheating chamber generally coextensive with the exhaust chamber an a final heating chamber generally coextensive with the fire tube.
Whitaker, U.S. Pat. No. 2,494,113 discloses improvements in furnaces used for the heating of buildings. In particular Whitaker teaches the introduction of the flame on a chord, i.e. the flame enters tangentially. He also discusses the notion of providing a spiral baffle plate which in effect directs the gases of combustion in a helical path around a plurality of four or more flues. The air to be heated enters the flues from an intake manifold passes through the flues being heated by the combustion gases and then passes into a hot air manifold at the top of the furnace for distribution by conventional means to the spaces to be heated.
Hoesman, U.S. Pat. No. 764,191 discloses a spiral draft configuration. The combustion gases are conveyed through pipes having a spiral arrangement. The spiral arrangement of the pipes induces a spiral draft, which he contends as being very effective in keeping up a rapid combustion. The air being heated ascends through the casing and the coiled pipes and is thoroughly and quickly heated by the hot combustion gases.